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bh=dVzlQsVNragLPJ6XHG4+yhjDcNqbMchdDd4G/Y+DVH0=; b=LJ4qykXNMXPTaoLCt9p9pSOiY+yUuJSJouBTWNrS/safQp7hqtraF/yxQxnsDJy2a+Zwh1 2AkhMWszionkoXrMUBsMdRJSA4ed8P3tgpbkWEiGUyLQnwpNJlRiEAUczGnhAC1avHNwLd o56J6Cs/X5jpx3wCt6FPVK84AvENKbE= X-MC-Unique: 5TOquhImOeyypwltrED4RQ-1 From: Maxim Levitsky To: qemu-devel@nongnu.org Subject: [PATCH v5 5/9] device-core: use atomic_set on .realized property Date: Sun, 13 Sep 2020 19:02:55 +0300 Message-Id: <20200913160259.32145-6-mlevitsk@redhat.com> In-Reply-To: <20200913160259.32145-1-mlevitsk@redhat.com> References: <20200913160259.32145-1-mlevitsk@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mlevitsk@redhat.com X-Mimecast-Spam-Score: 0.001 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=207.211.31.81; envelope-from=mlevitsk@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/13 09:40:16 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -37 X-Spam_score: -3.8 X-Spam_bar: --- X-Spam_report: (-3.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.695, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Fam Zheng , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= , Eduardo Habkost , "Michael S. Tsirkin" , Maxim Levitsky , Stefan Hajnoczi , Paolo Bonzini Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" Some code might race with placement of new devices on a bus. We currently first place a (unrealized) device on the bus and then realize it. As a workaround, users that scan the child device list, can check the realized property to see if it is safe to access such a device. Use an atomic write here too to aid with this. A separate discussion is what to do with devices that are unrealized: It looks like for this case we only call the hotplug handler's unplug callback and its up to it to unrealize the device. An atomic operation doesn't cause harm for this code path though. Signed-off-by: Maxim Levitsky Reviewed-by: Stefan Hajnoczi --- hw/core/qdev.c | 19 ++++++++++++++++++- include/hw/qdev-core.h | 2 ++ 2 files changed, 20 insertions(+), 1 deletion(-) diff --git a/hw/core/qdev.c b/hw/core/qdev.c index 28e5fff5ed..97165a556d 100644 --- a/hw/core/qdev.c +++ b/hw/core/qdev.c @@ -933,7 +933,25 @@ static void device_set_realized(Object *obj, bool valu= e, Error **errp) } } =20 + atomic_store_release(&dev->realized, value); + } else if (!value && dev->realized) { + + /* + * Change the value so that any concurrent users are aware + * that the device is going to be unrealized + * + * TODO: change .realized property to enum that states + * each phase of the device realization/unrealization + */ + + atomic_set(&dev->realized, value); + /* + * execute full memory barrier to ensure that concurrent users + * see this update prior to any other changes to the device + */ + smp_mb(); + QLIST_FOREACH(bus, &dev->child_bus, sibling) { qbus_unrealize(bus); } @@ -948,7 +966,6 @@ static void device_set_realized(Object *obj, bool value= , Error **errp) } =20 assert(local_err =3D=3D NULL); - dev->realized =3D value; return; =20 child_realize_fail: diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h index 7f91c8ead4..1769cfe2a5 100644 --- a/include/hw/qdev-core.h +++ b/include/hw/qdev-core.h @@ -165,6 +165,8 @@ struct NamedClockList { /** * DeviceState: * @realized: Indicates whether the device has been fully constructed. + * When accessed outsize big qemu lock, must be accessed with + * atomic_load_acquire() * @reset: ResettableState for the device; handled by Resettable interface. * * This structure should not be accessed directly. We declare it here --=20 2.26.2